A stroboscopic image (multi-stroboscopic image) is known which is produced by capturing a multiple image of a moving object with a stationary camera and shows, as a single image (photograph) a manner of movement of the object. In the days of film cameras, such a stroboscopic image was taken by performing plural strobe light emissions on a moving object during a long-term exposure. However, since digital cameras have become widely used, such a stroboscopic image can be generated by computer image processing performed by the digital camera.
As a conventional method for generating stroboscopic image by image processing, there is proposed a method to determine object positions by extracting object portions from images, the object portions not overlapping with one another. An example of such method is disclosed in Japanese Patent No. 3,793,258. There is also being proposed a method to determine object positions, the method in which a time point, which appears to be used a background image for generating the stroboscopic image, is specified from a video image. An example of such method is disclosed in Japanese Patent No. 3,569,992 (counterpart U.S. publication is: U.S. Pat. No. 5,721,692).
In the conventional methods described above, object positions in images cannot be determined until area information is acquired for all the captured images in a case where the frame rate or the object size varies during the consecutive image capturing or video image capturing. As a result, in generating a stroboscopic image from images consecutively captured or from a video image, a considerable time is required to select images to be used for generating a stroboscopic image. Accordingly, a stroboscopic image cannot be generated at high speed when the conventional methods are used.